1. Field of the Invention
This invention relates to improvement in automotive cooling fan assemblies and, in particular, to a mechanical lock mechanism to override the operation of a conventional fan drive clutch.
2. Brief Description of the Prior Art
Most automotive engines are presently provided with a drive clutch between the cooling fan and its drive shaft. Commonly, the drive shaft bears a flange on one end which is secured by screw fasteners, i.e., bolts and the like to the hub of the water pump. The cooling fan is mounted on the fan clutch housing which is carried on the opposite end of the fan drive shaft. The fan clutch housing is bolted or otherwise secured to the spider of the cooling fan. Typically, the drive shaft bears a drive plate within the clutch housing which is surrounded by a fluid, and the drag of the plate on the fluid is the coupling between the drive shaft and clutch housing. Centrifical forces developed by rotation of the clutch housing during engine operation serve to pump the fluid from the housing depleting oil from the vicinity of the drive shaft plate and permitting greater slip in the clutch coupling in response to the setting of a control valve. In the more elaborate and expensive clutches, the clutch housing bears a temperature responsive element such as a bi-metallic spring which controls the position of the fluid control valve, closing the valve when the ambient temperature rises to maintain more fluid in the vicinity of the drive plate and reduce the slip between the drive plate and the fluid-filled interior of the housing.
Many of the automotive fan drive clutches lack the aforedescribed temperature responsive valve and, are responsive only to engine speed, providing maximum slip at high engine speeds and minimal slip at low engine speeds.
The aforedescribed fan drive clutches generally provide for efficient engine operation when new or when maintained in good condition or when the vehicle is operated at highway speeds. Often, however, the operation of the clutch deteriorates with age and the engines of older vehicles have a pronounced tendency to overheat with loading. Since the fan drive clutch is relatively expensive, this item is not frequently serviced or replaced and older vehicles frequently suffer overheating problems attributable to a faulty fan clutch. Additionally, fan drive clutches, even when new or when properly maintained, are ill designed for operation on vehicles that are operated at extended periods in low gears with high engine speeds, such as experienced when pulling heavy trailers and/or during off-road driving. In these applications, the centrifical type clutches permit a high degree of slip in the clutch drive to the cooling fan and inadequate cooling frequently occurs, resulting in overheating.
It is, therefore, desirable to provide lock means which can be readily and simply installed on a vehicle to provide a positive, mechanical lock between the cooling fan and the fan drive shaft. Desirably, such lock means should be readily removable from the vehicle and should not require any substantial or significant modifications to the cooling fan assembly. Because of the high rotational speeds of the fan drive shaft and cooling fan, the lock means should have positive means to secure it against any accidental dislodgement.